The present invention relates to a current injection logic device with a Josephson diode network, which are also called Josephson junctions. It more particularly applies to the production of logic AND or OR gates, which can more particularly be used for producing cryogenic computers.
Various types of Josephson effect logic devices are known and are described in the article by T. Gheewala, entitled "Josephson Logic Devices and Circuits", published in the journal IEEE Translactions on Electronic Devices, vol. ED27, 1980, pp. 1857 to 1869. One of these is constituted by logic devices having loops provided with inductors, which have a functional role in these devices and which consequently have the disadvantage of occupying a large surface area, which is prejudicial to their use in producing integrated logic circuits.
It is also possible to consider another group of logic devices using assemblies of Josephson diodes and resistors and which offers better integration possibilities. Reference is therefore made to the assembly diagrammatically shown in FIG. 1 and which constitutes a logic AND gate. The latter has a Josephson diode network formed from three parallel-connected branches, and respectively having the pairs of series connected Josephson diodes (J.sub.11, J.sub.21), (J.sub.12, J.sub.22) and J.sub.13, J.sub.23). Diodes J.sub.11, J.sub.12, J.sub.13 are connected to a first main electrode B.sub.1 and diodes J.sub.21, J.sub.22 and J.sub.23 are connected to a second main electrode B.sub.2, which is earthed. The device also has two inputs E.sub.1 and E.sub.2. Input E.sub.1 is connected to the intermediate electrode A.sub.1 between diodes J.sub.11 and J.sub.21 and input E.sub.2 is connected to intermediate electrode A.sub.2 between diodes J.sub.12 and J.sub.22. Finally, the AND gate has an output S, which is connected to the first main electrode B.sub.1 and which is also closed on its characteristic impedance of equivalent resistor R.sub.L1. Electrodes A.sub.1 and A.sub.2 are connected to the first main electrode B.sub.1, respectively by shunt resistors R.sub.1 and R.sub.2, which are respectively smaller than the leakage resistors of diodes J.sub.21 and J.sub.22 and also smaller than the equivalent resistor R.sub.L1. Diodes J.sub.11, J.sub.21, J.sub.12 and J.sub.22 have the same critical current I.sub.0 and diodes J.sub.13 and J.sub.23 have the same critical current, which is e.g. equal to 3I.sub.0.
The devices shown in FIG. 1 operates in the following way. In its initial state, the six Josephson diodes are superconductive. Output S is at logic state 0, no current being supplied to said output. Under the action of a control current of intensity I.sub.C1 exceeding 2I.sub.0, injected by input E.sub.1 into the device, diodes J.sub.11 and J.sub.21 switch from a zero voltage state to a non-zero voltage state corresponding to a high impedance state. Current I.sub.C1, injected into electrode A.sub.1, is then deflected by means of shunt resistor R.sub.1 to the first main electrode B.sub.1, from which it is divided up between branches respectively having the pairs (J.sub.12, J.sub.22) and (J.sub.13, J.sub.23). Output S remains at logic state 0.
Under the effect of another control current, the intensity I.sub.C2 exceeding 2I.sub.0, injected by input E.sub.2 into the device, diodes J.sub.12 and J.sub.22 are successively switched and the current I.sub.C2, injected into electrode A.sub.2, is then deflected by means of shunt resistor R.sub.2 towards the first main electrode B.sub.1, from where it is divided up between the branches having respectively pairs (J.sub.11, J.sub.21) and (J.sub.13, J.sub.23). Output S still remains at logic state 0. However, under the combined effect of currents I.sub.C1 and I.sub.C2, diodes J.sub.11, J.sub.21 J.sub.12 and J.sub.22 are switched. Currents I.sub.C1 and I.sub.C2 are then deflected, respectively by means of shunt resistors R.sub.1 and R.sub.2, towards the first main electrode B.sub.1 and diodes J.sub.13 and J.sub.23 are consequently switched into a non-zero voltage state. Therefore currents I.sub.C1 and I.sub.C2 are deflected towards output S and produce there an output current I.sub.S. Thus, this output then passes to logic state 1. The device shown in FIG. 1 consequently operates as an AND gate.
It is also possible to conceive an OR gate using an assembly of Josephson diodes and resistors. Instead of connecting the intermediate electrodes A.sub.1 and A.sub.2 of the aforementioned device to the first main electrode B.sub.1, via shunt resistors R.sub.1 and R.sub.2, said intermediate electrodes are connected to the second main electrode B.sub.2 via resistors R.sub.1 and R.sub.2. A polarizing current of intensity I.sub.P equivalent to 4I.sub.0 for example, is then introduced into the first main electrode B.sub.1. The injection of a current having an intensity higher than I.sub.0 into one of the inputs E.sub.1 and E.sub.2, combined with the injection of polarizing current I.sub.P, leads to the switching of diodes J.sub.11, J.sub.12 and J.sub.13, which leads to a polarizing current I.sub.P being introduced into output S in order to constitute an output current I.sub.S.
Thus, the logic devices of the other group considered and of which two examples have been given hereinbefore, require resistors to operate and consequently have the disadvantage of a relatively long production cycle, because such a cycle must involve several stages relating to the production of the various resistors. Moreover, these devices have another disadvantage. The resistors incorporated therein give them very low damping coefficients and consequently a considerable turn-on delay, which reduces the dynamic performances, i.e. the speed of the devices in question, of. the article by P. Migny and B. Placais, entitled "Turn-on Delay for Josephson Logic Devices with High Damping" and published in Electronic Letters, vol. 18, no. 18, September 1982, pp. 777 to 779.